The Applicant has developed a range of Memjet® inkjet printers as described in, for example, WO2011/143700, WO2011/143699 and WO2009/089567, the contents of which are herein incorporated by reference. Memjet® printers employ one or more stationary inkjet printheads in combination with a feed mechanism which feeds print media past the printhead in a single pass. Memjet® printers therefore provide much higher printing speeds than conventional scanning inkjet printers.
All inkjet printheads need to be capped during non-printing periods to prevent nozzles from drying out. Typically, a printhead capper comprises a compliant perimeter seal engaged with a capping surface of the printhead so as to provide a sealed humid environment for the nozzles. Nevertheless, some drying of the nozzles is inevitable and printers typically perform remedial maintenance operations after uncapping to ensure that the printhead is ready to print. For example, a forced positive pressure prime may be used to unblock any blocked nozzles (see, for example, U.S. Pat. No. 8,845,083, the contents of which are herein incorporated by reference). Additionally or alternatively, the printhead nozzles may eject ink into a spittoon to ensure each nozzle is hydrated and primed with ink.
It is desirable to maximize the humidity of the nozzle environment when a printhead is capped. In this way, the remedial measures required for full nozzle health after uncapping can be minimized. Minimizing such remedial measures not only shortens the ‘wake-up’ time of the printer, but also reduces the amount of ink consumed for non-printing purposes during spitting and pressure priming.
Notwithstanding the primary requirement for printhead cappers to maximize the humidity of the nozzle environment, cappers paradoxically incorporate a small breather hole (or vent hole), which allows water vapor to escape from the capped volume. The breather hole is deemed necessary in conventional cappers to equalize the pressure of the capped volume with atmospheric pressure. Pressure-equalization prevents a number of undesirable consequences during capper usage e.g. suctioning the capper to the making it difficult to uncap; suctioning excessive volumes of ink from the printhead into the capper; developing overpressure in the capper, which can push ink into the printhead and deprime nozzles etc.
In the absence of a breather hole, overpressure or suction in the capper may be caused by, for example, mechanical movement of the capping and uncapping, temperature changes causing trapped air inside the capper to expand contract, changes in atmospheric pressure etc.
Typically, the breather hole is designed to minimize vapor losses using, for example, a serpentine or labyrinthine path. However, even with such measures, a degree of vapor loss is inevitable over long periods and it would be desirable to minimize vapor losses even further whilst still allowing facile capping and uncapping.